Abstract
BackgroundWe 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.ResultsThe 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.ConclusionOur 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.
Highlights
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
The main requirement for an orthomode transducer (OMT) used in radioastronomy experiment dedicated to reveal polarized patterns of the Galactic radio continuum, like the Galactic Emission Mapping (GEM) project (Torres et al 1996), is a high isolation between the output ports across the intended bandwidth
The main goal of the GEM project is to characterize the Galactic emission in total intensity and polarization between 408 MHz and 10 GHz, by producing astrophysical foreground templates to decontaminate Cosmic Microwave Background Radiation maps (see Tello et al (2013) for recent results at 2300 MHz)
Summary
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. The main requirement for an OMT used in radioastronomy experiment dedicated to reveal polarized patterns of the Galactic radio continuum, like the Galactic Emission Mapping (GEM) project (Torres et al 1996), is a high isolation between the output ports across the intended bandwidth. Galactic emission in the GEM frequency bands at 5 and 10 GHz is dominated by synchrotron radiation In these bands, the radio emission has a high degree of linear polarization and interstellar Faraday effects are still negligible. In this article we describe an OMT that can be classified as Septum-Branching OMT class 1, following the classification presented in (Bøifot 1991; Uher et al 1993) It was developed for a pseudo-correlation polarimeter, suitable for a Ferreira et al SpringerPlus (2016) 5:2069 bandwidth of 400 MHz centered at 5 GHz and having a measured sensitivity of about 1:6 mk/√s (Bergano et al 2007)
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