Turnstile Polarizer: A Broadband Continuously Reconfigurable Polarization Modulator—Part I: Principle, Design, and Analysis

This two-part article presents a new-type waveguide polarizer, referred to as a turnstile polarizer (TP), which achieves precise arbitrary polarization synthesis within a broad bandwidth. In this part, the concept, operating principle, performance analysis, and design process of the TP are illustrated. Output modes with arbitrary polarization can be reconfigured by relative rotation between the TP and linear polarization (LP) probe, following a point-to-point mapping from the equatorial to the meridian on the Poincaré sphere. Moreover, a combination of hybrid phase shifters is employed to achieve excellent broadband phase balance based on an error cancellation mechanism. The regulation strategy adopted utilizes orthogonal differential voltage vectors with a steerable power ratio in a turnstile junction (TJ) to realize phase-compensation-enabled arbitrary degenerate polarization synthesis. The design procedure and simulated result of a W-band based on a gap waveguide (GW) are illustrated. The TP exhibits a 37.8% impedance bandwidth (75–110 GHz) with a return loss (RL) exceeding 25 dB and an insertion loss (IL) below 0.1 dB. For operations with arbitrary polarization states, the in-band AR error remains within 1 dB, and the polarization conversion ratio (PCR) exceeds 99%. The proposed TP provides a cost-effective passive polarization modulation (PoM) solution, offering excellent flexibility and precision in polarization regulation while achieving a broad bandwidth and high efficiency. Additionally, the TP features robustness, a low profile, manufacturing simplicity, and assembly convenience, making it suitable for sub-THz applications.