210-365 GHz 90° Differential Phase Shifter for Wideband Circular Polarizer

• Published in: IEEE transactions on terahertz science and technology Vol. 12; no. 5; pp. 527 - 534
• Main Authors: Masui, Sho, Hasegawa, Yutaka, Ogawa, Hideo, Kojima, Takafumi, Onishi, Toshikazu
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.09.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidths; Broadband; Dual polarization (waves); Event horizon; Phase shift; Phase shifters; Polarization; polarization splitter; Polarizers; radio astronomy; Receivers; submillimeter-wave waveguide circuits; Telescopes; Transducers; Waveguide transitions; Waveguides; Wideband
• ISSN: 2156-342X; 2156-3446
• DOI: 10.1109/TTHZ.2022.3191851

In this article, a wideband 90° differential phase shifter in the 210-365 GHz band with a fractional bandwidth of 54% was designed, fabricated, and measured to develop a wideband circular polarizer for millimeter/submillimeter wavelengths. To achieve a wide bandwidth, we designed a 90° differential phase shifter with a flat phase-difference characteristic by combining three different types of 90° differential phase shifters to cancel out the frequency dependence of the phase difference between the two polarizations. The developed phase shifter has a phase difference of 90 ± 6° and a return loss better than 17 dB for both polarizations over the frequencies 210-365 GHz, in addition to waveguide transitions necessary for S -parameter measurements. The developed phase shifter can be used as an alternative for achieving simultaneous observations of dual-polarization signals at 230 and 345 GHz, as proposed by the next-generation event horizon telescope, which aims to observe black holes.