Novel Miniaturized Antenna with a Highly Tunable Complex Input Impedance for Capsules

A novel miniaturized antenna with a complex input impedance that can be flexibly tuned is proposed for ingestible capsules in this work. The antenna is circular in shape with a diameter of 10 mm and works in the industrial, scientific, and medical (ISM) 2.45 GHz band. Owing to the use of a novel Pi -match and the utilization of coupling between the antenna end and feed point, both the real and imaginary parts of the input impedance of the proposed antenna can be tuned flexibly in a wide range. In addition, the input impedance varies smoothly with frequency, which implies a wide bandwidth. Hence, the proposed antenna can be conjugately matched to a transceiver directly without using extra impedance matching network. The operating principle of the proposed antenna is analyzed in-depth through the equivalent circuit and parametric study. To demonstrate the advantages, the proposed antenna is then compared with a widely used miniaturized antenna with T-match. Finally, the prototypes are fabricated and measured to experimentally validate the proposed design.