Polarization-Converting Metasurface Inspired Dual-Band Dual-Circularly Polarized Monopole Antennas for Off-Body Communications

This letter investigates a novel technique to achieve circular polarizations (CPs) at 2.45 GHz ISM and 3.5 GHz WiMAX bands. The behavior is achieved by incidenting an $x$-polarized wave from a monopole antenna (MA) on a polarization-converting metasurface (PCMS). The PCMS operates in TM$_{10}$ and TM$_{20}$ modes that generate dual frequency bands and reflect a 90° phase-shifted y-polarized wave that, when combined with the 0° phase containing $x$-polarized wave, generates CP. To attain four separate combinations of phase-shift in terms of +90° and −90° in dual bands, four distinct 2×2 PCMSs are designed, which are designated as MS$_{1}$, MS$_{2}$, MS$_{3}$, and MS$_{4}$. The MS$_{1}$-based MA (A$_{1}$) produces left-hand CP (LHCP), whereas the MS$_{2}$-based MA (A$_{2}$) produces right-hand CP (RHCP) in both frequency bands. On the other hand, the MS$_{3}$-based MA (A$_{3}$) produces RHCP in the lower band (LB) and LHCP in the higher band (HB), whereas the MS$_{4}$-based MA (A$_{4}$) produces LHCP in the LB and RHCP in the HB. A$_{3}$ is fabricated and measured, and the results are very close to the simulations. Each antenna has a wide impedance bandwidth, a high gain, and high efficiency with a low specific absorption rate (SAR) in the desired bands, which justifies their suitability for off-body communication.