Circularly Polarized Miniaturized Implantable Antenna for Leadless Pacemaker Devices

A compact circularly polarized (CP) implantable antenna working at 915 MHz, at the industrial, scientific, and medical (ISM) band, is developed in this article. The proposed radiator is based on a fully planar and low-profile patch antenna with a ground plane and different slots but without any via holes, which makes the structure a good candidate for implantable devices. The circular polarization is achieved by means of introducing a surrounding and asymmetrical U-shaped structure. A meander line has been included in the inside of the U-shaped structure to increase the electrical length of the antenna without increasing its mechanical dimensions. An impedance bandwidth of 18.9% from 810 to 980 MHz and an axial ratio of 17.2% from 850 to 1010 MHz have been achieved. The proposed antenna has a compact size of 5.2 x 5.6 x 0.25 mm(3), which seems to be the smallest antenna over the recently reported implantable antennas. In addition, the proposed antenna achieves a relatively high gain value of -23 dBi.