A Compact Broadband Circularly Polarized Patch Antenna Using Ladder Slots and Grounded Capacitors for MedRadio-Band Applications

This paper presents a compact broadband circularly polarized (CP) implantable antenna at the Medical Device Radio communications Service (MedRadio) band (401-406 MHz). The proposed antenna is designed by utilizing the ladder structure slots along with shorting strategy on the radiating patch, and embedding the chip capacitors loading on the ground plane. The proposed antenna’s performances are tested via numerical simulations in a three-layer phantom model. The prototypes are experimentally measured with minced pork as well as in muscle-mimicking gel, and the results show a good agreement. The experiment results indicated that the proposed CP antenna has a small overall size of 9.5 mm
$\times9.5$
mm
$\times0.64$
mm (57.76 mm
³
) with a broad impedance matching of 25% from 350 MHz to 469 MHz, a realized gain of -31.2 dBi, and produces a wide axial ratio (AR) bandwidth of 30.5% (123 MHz with ranger from 337 MHz to 460 MHz). Moreover, the maximum specific absorption rate (SAR) value also complies with the IEEE standard safety requirements. To the best of our knowledge, the proposed CP antenna is the compactest dimension with wider impedance matching, and greater gain value (without using superstrate) and obtain CP with widest AR bandwidth compared to previously reported works in the MedRadio band.