A Novel Concept of TE₂₀-Mode 90∘ Waveguide Twist With Mode Filtering Characteristics

We present a novel TE <tex-math notation="LaTeX">₂₀</tex-math> -mode 90 <tex-math notation="LaTeX">∘</tex-math> waveguide twist concept for millimeter-wave (mm-wave) and terahertz (THz) applications. This waveguide twist has the unique characteristic of mode filtering; that is, only the desired TE <tex-math notation="LaTeX">₂₀</tex-math> mode can be rotated and output, the fundamental TE <tex-math notation="LaTeX">₁₀</tex-math> mode, and higher order modes will be reflected. In the design, the input/output (I/O) channels are orthogonal oversized waveguides, the TE <tex-math notation="LaTeX">₂₀</tex-math> mode is converted into a cross-waveguide (cross-WG) with gradually changed arm lengths. Broad bandwidth (BW) and high efficiency can be easily achieved in a compact size. To verify the proposed concept, two 160–270-GHz prototypes based on rectangular waveguides (RWGs) and groove gap waveguides (GGWs) were designed, fabricated, and measured. The RWG-based prototype was milled in one metal block, while the GGW-based one was fabricated in two metal split blocks. The measured results reveal that the two prototypes achieve average insertion losses of 0.21 and 0.36 dB for the interested TE <tex-math notation="LaTeX">₂₀</tex-math> mode, and minimum suppressions of 45 and 35 dB for the unwanted TE <tex-math notation="LaTeX">₁₀</tex-math> mode over the desired frequency band. The features of polarization rotation and mode filtering make the proposed TE <tex-math notation="LaTeX">₂₀</tex-math> -mode waveguide twist be a candidate for compact, broadband, and efficient waveguide systems.