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ALMA MEMO #425
The Bøifot Orthomode Junction
Edward J. Wollack (NASA/GSFC), Wes Grammer (NRAO), Jeff Kingsley (NRAO)
2002/05/22
Keywords: Orthomode Transducer, Orthomode Junction, Polarization Diplexer,
Waveguide Junction
Wideband dual-polarization performance is desired for low-noise receivers and radiometers at centimeter and millimeter wavelengths. The use of a waveguide orthomode transducer (OMT) can increase spectral coverage and sensitivity while reducing exit aperture size, optical spill, and instrumental polarization offsets. For these reasons, an orthomode junction is favored over a traditional quasi-optical wire grid for focal plane imaging arrays from a systems perspective. The fabrication and performance of wideband symmetric Bøifot OMT junctions at K-, Ka-, Q-, and W-bands are described. Typical WR10.0 units have an insertion loss of <0.2 dB, return loss ~20dB, and >40dB isolation over a >75-to-110 GHz band. The OMT operates with reduced ohmic losses at cryogenic temperatures.
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Last modified: 2002-05-22
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