A Turnstile Quad-Ridge Orthomode Transducer (OMT) for Octave-Bandwidth Receiver Front-Ends (24-51 GHz)

• Published in: IEEE transactions on microwave theory and techniques Vol. 71; no. 11; pp. 1 - 16
• Main Authors: Henke, Doug, Kelly, Neal, Marshall, Kyle, Wevers, Ivan, Knee, Lewis B. G.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: <inline-formula xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <tex-math notation="LaTeX"> Q</tex-math> </inline-formula>-band; Bandwidth; Bandwidths; Double-ridge waveguide; Dual polarization (waves); Feeds; Insertion loss; octave bandwidth; orthomode transducer (OMT); Polarization; quad-ridge waveguide; quad-ridge waveguide turnstile junction; Radio astronomy; Radio telescopes; Receivers; Receivers & amplifiers; Rectangular waveguides; ridge waveguide; Transducers; Waveguide components; Waveguide junctions; wide bandwidth receivers
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2023.3267544

We report on the design, fabrication, and measured results of a turnstile quad-ridge orthomode transducer (OMT) suitable for millimeter-wavelength receivers used in radio telescopes for astronomy. The quad-ridge OMT is directly compatible with a quad-ridge feed horn to implement dual-polarization low-noise receivers that exceed the single-mode bandwidth of a rectangular waveguide. Using a bandwidth of 24-51 GHz, the OMT demonstrated an insertion loss of 0.3-0.4 dB along with cross-polarization leakage and isolation below <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>40 dB. An OMT is a key part of a dual polarization receiver front-end, and our long-term goal is to realize low-noise, wideband receivers for radio astronomy utilizing ridge waveguides throughout the entire front-end. Design details are provided for each ridge waveguide feature within the OMT, including a quad-ridge waveguide turnstile junction, <inline-formula> <tex-math notation="LaTeX">E</tex-math> </inline-formula>-plane bend, and <inline-formula> <tex-math notation="LaTeX">E</tex-math> </inline-formula>-plane T-junction. To facilitate future layouts and integration, additional ridge waveguide component designs have been included for a 3-dB coupler, <inline-formula> <tex-math notation="LaTeX">H</tex-math> </inline-formula>-plane bend, and <inline-formula> <tex-math notation="LaTeX">H</tex-math> </inline-formula>-plane T-junction.