Waveguide Coupler With Polarized Rotation Characteristics for Terahertz Applications

Abstract

In this work, a class of innovative waveguide couplers with polarized rotation characteristics are proposed and demonstrated for the first time. Different from all conventional waveguide couplers, the proposed couplers involve two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -plane ports and two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$</tex-math> </inline-formula> -plane ports, herein referred to as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -plane and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$</tex-math> </inline-formula> -plane (EH) waveguide couplers. The couplers are set to directly convert <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -plane to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$</tex-math> </inline-formula> -plane port or vice versa, without resorting to any conventional waveguide twist whatsoever, thereby reducing integration complexity, structure size, and associated losses, compared to the conventional counterparts. To validate the proposed topology, two experimental prototypes of the EH waveguide couplers are studied, designed, fabricated, and measured. The first is an EH hybrid waveguide coupler and the second is an EH cruciform waveguide coupler. The measured results show that the return loss and isolation of the hybrid waveguide coupler are better than 20 dB. In addition, the amplitude imbalance and phase imbalance are lower than 0.5 dB and 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> , respectively, over a frequency range of 140–160 GHz. The measured EH cruciform waveguide coupler shows that the return loss and isolation are better than 18 and 21 dB, respectively. Over the operating frequency range of interest covering 140–160 GHz, the amplitude imbalance and phase imbalance are lower than 0.5 dB and 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> , respectively. The length of both waveguide couplers is only 0.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda$</tex-math> </inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $</tex-math> </inline-formula> is the wavelength at the center frequency. To the best of our knowledge, such EH waveguide couplers are the most compact waveguide couplers ever demonstrated so far. Therefore, the proposed EH waveguide couplers present excellent candidates for compact terahertz (THz) integrated waveguide circuits and systems.