title: A C-band broadband ortho-mode transducer for radioastronomy polarimetry.
abstract: BACKGROUND
  We describe the design, the construction and performance of a narrow band ortho-mode transducer, currently used in the 5 GHz polarimetric receiver of the Galactic Emission Mapping project.
  
  
  RESULTS
  The ortho-mode transducer was designed to achieve a high degree of transmission within the 400 MHz of the GEM band around the 5 GHz (4.8-5.2 GHz). It is composed of a circular-to-square waveguide transition, a septum polarizer, a thin waveguide coupler and a smooth square-to-rectangular waveguide transition with custom waveguide bends to the output ports.
  
  
  CONCLUSIONS
  Our simulations and measurements show a very low level of cross-polarization of about -60 dB and a good impedance match for all three ports (S11; S22; S33 < -30 dB) with only 0:25 dB of insertion loss offset across the 400 MHz (4.8-5.2 GHz) of the reception bandwidth.
authors.affiliation: Laboratório de Cosmologia e Astrofísica, Instituto de Física, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Asa Norte, Brasília, 70919-970 Brazil.
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Ferreira
authors.affiliation: Divisão de Astrofísica - DAS, Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1.758, Jd. Granja, São José dos Campos, SP CEP 12227-010 Brazil.
authors.forename: Camilo
authors.initials: C
authors.lastname: Tello
authors.affiliation: Wiseware Engineered Solutions, Zona Industrial da Mota, Rua 12, Lote 51, Fração E, 3830-527 Gafanha da Encarnação, Portugal.
authors.forename: Miguel
authors.identifier: 0000-0002-5191-7826
authors.initials: M
authors.lastname: Bergano
authors.affiliation: Divisão de Astrofísica - DAS, Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1.758, Jd. Granja, São José dos Campos, SP CEP 12227-010 Brazil.
authors.forename: Thyrso
authors.initials: T
authors.lastname: Villela
authors.affiliation: ENGAGE SKA, Instituto de Telecomunicações, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
authors.forename: Domingos
authors.initials: D
authors.lastname: Barbosa
authors.affiliation: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50-5005, Berkeley, CA 94720 USA ; Université Paris-Diderot APC, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France.
authors.forename: George F
authors.initials: GF
authors.lastname: Smoot
keywords: Ortho-mode transducers; Polarimeters; Radioastronomy