Linear-Cross and Linear-Circular Polarization Converter in the THz Regime

Abstract

The design of novel reflective type multiband dual polarizers is proposed in this dissertation. The proposed structures can perform linear to cross as well as linear to circular conversion in the THz regime. The designed structures consist of a thin gold coated Frequency Selective Surface (FSS) printed on top of a polyamide substrate, with a thin gold film as the ground plane. The square loop FSS exhibits Linear-Circular conversion with an Axial Ratio (≤ 3dB) from 0.49-0.50 THz, 0.60-0.83 THz, 1.16-1.62 THz and 1.81-1.85 THz. In addition, it also performs the Linear-Cross conversion with a minimum 90% Po- larization Conversion Ratio (PCR) from 0.53-0.56 THz, 0.92-1.07 THz and 1.69- 1.75THz. The polarizer unitcell architecture is compact with structural dimensions of 0.121×0.121×0.041 λ 3 L , where λ L is the lowest operating frequency’s free-space wavelength. The circular loop FSS shows Linear-Cross conversion with a minimum 90% Polar- ization Conversion Ratio (PCR) from 0.62- 0.65THz, 0.98-1.10THz and 1.74-1.80THz. Furthermore it perform Linear-Circular conversion with Axial Ratio (≤ 3dB) from 0.58-0.59THz, 0.69-0.90THz, 1.18-1.67THz and 1.87- 1.90THz. This unitcell has a structural dimensions of 0.153×0.153×0.039 λ 3 L , where λ L is the lowest operating frequency’s free-space wavelength. Multiple surface plasmonic resonance is the phenomenon behind the conversion at different frequency bands. The metasurface’s performance is stable up to 45 0 for both Transverse Electric (TE) and Transverse Magnetic (TM) oblique incidences. Making this design compact, with angular stable multi-band multi conversion ability that will significantly impact the THz applications in real-time.