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 TM10 and TM20 modes that generate dual frequency bands and reflect a 90 degrees phase-shifted y-polarized wave that, when combined with the 0 degrees phase containing x-polarized wave, generates CP. To attain four separate combinations of phase-shift in terms of +90 degrees and -90 degrees in dual bands, four distinct 2x2 PCMSs are designed, which are designated as MS1, MS2, MS3, and MS4. The MS1-based MA (A(1)) produces left-hand CP (LHCP), whereas the MS2-based MA (A(2)) produces right-hand CP (RHCP) in both frequency bands. On the other hand, the MS3-based MA (A3) produces RHCP in the lower band (LB) and LHCP in the higher band (HB), whereas the MS4-based MA (A(4)) produces LHCP in the LB and RHCP in the HB. A3 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.