An Implantable Wideband Circularly Polarized Microstrip Patch Antenna via Two Pairs of Degenerate Modes

This paper presents a design approach for developing a wideband circularly polarized (CP) microstrip patch antenna (MPA) embedded in the human body. To achieve this goal, a pair of high-order degenerate modes (TM30 and TM03) in MPA have been excited and lowered for resonance in proximity to a pair of fundamental degenerate modes (TM10 and TM01). The proper disturbance of these two pairs of radiative resonant modes can contribute to the generation of two CP radiating waves at two near-by operating frequencies, aiming to realize CP radiation in a wide operating band covered by these two frequencies. A novel implantable wideband CP MPA is proposed and developed due to the emergence of two minima in the axial-ratio (AR) frequency response. The designed MPA is then demonstrated to tremendously achieve the wide 3-dB AR bandwidth which covers the 2.4 to 2.48 GHz ISM-band in the cubic human skin model. Moreover, the proposed CP MPA shows good tolerance to the variety of tissue according to our study on sensitivity and model integrity. Finally, the designed CP MPA is fabricated and tested, and a good agreement exists between measured and simulated results in a wide frequency region.