Multiband dual polarization conversion metasurface based on three-quarter circular-shape in the terahertz regime

Multifunctional THz meta-devices are the demand of modern communication systems and have received a lot of attention recently. Most studies have concentrated on either linear-to-linear or linear-to-circular polarization conversion. However, to simultaneously achieve both in a wide bandwidth with high conversion efficiency remains a key factor. This paper introduces a reflective-type metasurface that operates in the THz frequency range and is capable of wideband dual-polarization conversion in multi-band. The basic component of the suggested converter consists of a three-quarter circular structure with an embedded X-shape. It has the ability to convert linearly polarized (LP) electromagnetic (EM) waves into circularly polarized (CP) waves with axial ratio less than 3 dB at frequencies of 1.83–2.93 THz (RHCP), 3.56–3.68 THz (LHCP), and 3.90–3.93 THz (LHCP), with fractional bandwidth (FBW) of 46.21 %, 3.31 %, and 0.76 %, respectively. The reflected waves exhibit a phase difference of approximately ±90° and ±270° between their cross- and co-coefficients. Besides, the converter is capable of achieving cross-polarization conversion (CPC) with a polarization conversion efficiency (PCE) that exceeds 97 % within the frequency ranges of 3.18–3.42 THz and 3.96–3.97 THz. The fractional bandwidth (FBW) for these ranges is 7.27 % and 0.25 % respectively. Furthermore, the investigation of surface current distribution patterns at different frequencies is conducted to analyze the conversion phenomena. The proposed polarizer has applications in electromagnetic measuring, THz sensing, antennas, imaging, and stealth technologies.