Broadband Gap Waveguide TE₁₀-to-TE₁₁ ^CP Mode Converter Based on Novel Phase-Compensation Turnstile Junction

In this article, we present a novel <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {TE}}_{10}$ </tex-math></inline-formula>-to-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {TE}}_{11}^{\text {CP}}$ </tex-math></inline-formula> (circularly polarized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {TE}}_{11}$ </tex-math></inline-formula>) mode converter topology based on a novel phase-compensation turnstile junction (TJ). The input <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {TE}}_{10}$ </tex-math></inline-formula> mode is split into four orthogonal channels through two stages of T-junctions and waveguide bends. A combination of inductive progressive and capacitive lagging phase shifters is introduced to achieve precise broadband phase compensation, following a phase error cancellation method. Four orthogonal signals with equal amplitude and a continuous phase difference of 90° are coupled in the TJ, generating a left-hand or right-hand <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {TE}}_{11}^{\text {CP}}$ </tex-math></inline-formula> mode. The mode converter can be constructed as either a single-layer or a double-layer structure. The single-layer structure features an ultralow profile and can be folded into a double-layer structure to reduce the overall radial size. According to the proposed network topology, a W-band mode converter based on a groove gap waveguide (GGW) is designed to effectively suppress energy leakage. The mode converter achieves 20-dB return loss (RL) and 2-dB axial ratio (AR) within the range of 72–113 GHz (44.3%). The prototype test results show excellent agreement with the simulation results across the entire W-band. The proposed GGW mode converter offers advantages, such as broad bandwidth, low loss, a low profile, and simple assembly, making it highly suitable for broadband millimeter-wave (mm-Wave) and sub-terahertz (sub-THz) circular polarization (CP) applications.