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.