## 1 Introduction
However, there has been a lack of devices with incident normal polarization with transmitted circularly polarized waves using metasurfaces. Such devices are required in systems where transmitted waves and incident waves need to be aligned. These systems are predominantly used in THz wireless communication systems, including satellite communication. Such devices fabricated on flexible substrates can be integrated with linearly polarized wide-band THz antennas to have a dual wide-band outgoing transmitted wave with opposite handedness. For dual-band LP-to-CP operation, there can be two possibilities: one is to use a wideband LP-to-CP converter so as to cover both required frequency bands. This is usually very difficult as it will practically increase the operational bandwidth for LP-to-CP operation. In the literature, a fractional bandwidth greater than 40% using transmissive metasurfaces has not been quoted so far. Moreover, no work has been reported to claim dual polarization in the same frequency band so as to cover applications requiring polarization diversity. The other possibility is to design a dual-band LP-to-CP converter that works over two different frequency bands with outgoing circular polarizations having opposite handedness in two bands. Dual-band polarization manipulators including cross polarization converters [33; 34] and LP-to-CP [35; 36; 37; 38; 39] converters have been proposed in the past. [PERSON] [34] et al. and [PERSON] et al. [35] reported metasurfaces based dual-band polarization converters for outgoing cross polarization. Recently reported dual band LP-to-CP polarization converters in microwave and THz bands are either complex or based on reflection type frequency selective surfaces [36; 37; 38; 39; 40]. Moreover, the operating bandwidths for the two bands are not wide. For example, [PERSON] et al. [36] reported dual-band transmission type LP-to-CP converter based on frequency selective surfaces. [PERSON] et al. [36] used four metallic layers to obtain 31.6% and 13.8% fractional bandwidths in C and Ku bands, respectively. The proposed structure's first and fourth metal layers consist of a split ring resonator bisected by a metallic strip; second and third metallic layers consist of a rectangular patch surrounded by a rectangular ring. [PERSON] et al. [37] presented the design of dual-band LP-to-CP using transmissive metasurfaces whose unit cell is composed of three metallic layers. The first and third layers consist of a metallic patch enclosed in a split ring resonator, whereas the second layer consists of a circle-eliminated square patch with a central rectangular metallic strip. In other research, 3 dB fractional bandwidths of about 5% and 8% for dual-bands in the Ka band have been achieved [37]. [PERSON] et al. [38] presented a dual-band LP-to-CP converter using Jerusalem cross and \"I\" dipole patterned frequency selective surfaces. Dual-band operation has been achieved for 29% and 12% fractional bandwidths. [PERSON] et al. [39] reported a multilayered radial-shaped resonator-based dual-band LP-to-CP in the Ka band and achieved 14.4% and 4% fractional bandwidths. The only work reported of a THz dual-band LP-to-CP [40] discusses a reflection-based double-layered structure with the bottom layer used as gold reflectors. Such devices achieve a wide band of operation but tend to block and interfere with feeding elements such as linearly polarized arrays. The transmission-based dual-wide-band LP-to-CP converter based on a simple configuration is still a challenging problem. In this paper, a novel dual-wide-band dual polarized LP-to-CP THz converter consisting of bi-layered transmissive metasurfaces has been presented. The proposed structure is novel, as it achieves dual-band widest transmission-based LP-to-CP operation with fractional bandwidths of 34% and 29% for the two bands in THz. Also, the structure consists of bi-layered metasurfaces. Dual-band operation is realized due to the excitation of two Eigenmodes generating phase delays.