Dual-Mode Implantable Antenna with Dual Bands for Omnidirectionally In-Body and Circularly Polarized Off-Body Communications

A dual-mode implantable antenna with dual bands for realizing multi functions in biomedical communications is designed. Based on microstrip antenna, slots and slow-wave structure is adopted, lowering frequency. Via loading shorting pins, different operating modes are excited. The proposed antenna operates at 915 MHz for omnidirectional in-body communication and at 2.45 GHz for circularly polarized (CP) off-body radiation. Via simulation, at 915 MHz, the antenna has an impedance bandwidth of 70 MHz (0.87 to 0.94 GHz, 7.7%). While at 2.45 GHz, the antenna has an impedance bandwidth of 300 MHz (2.38 to 2.68 GHz, 11.3%), and a 3-dB axis ratio (AR) bandwidth of 130 MHz (2.38 to 2.51 GHz, 5.3%). In the far field, at 915 MHz, the proposed antenna has a peak gain of −28.2 dBi and its half-power beamwidth (HPBW) covers 109° in E-plane with an out-of-roundness of 0.44 dB in H-plane. And at 2.45 GHz, the antenna has a maximum gain of −22.9 dBi with a HPBW of 77° and a 3-dB AR beamwidth of 80°.