Compact wideband bowtie dipole orthomode transducer

Abstract

A compact wideband orthomode transducer (OMT) with an octave bandwidth is proposed for a 0.56‐1.12 GHz receiver system in the five hundred meter aperture spherical radio telescope. The OMT operates in a cryostat at a temperature of 70 K and therefore it is critical to minimize its dimension while insuring good electrical properties. The complete OMT comprises 2 bowtie dipoles orthogonally arranged in a circular waveguide. Because of the innovative structure, competing modes, TM01 TE21, and TE01, have been effectively suppressed, and the bandwidth of the dominate mode TE11 has achieved to 2.08:1. The final optimized OMT has a length of 300 mm, shorter than a half of the popular quardruple‐ridged waveguide OMT. Measurements at room temperature agree well with simulation results, with a reflection coefficient below −10 dB for both polarizations and cross‐coupling levels of −30.5 dB over the whole required frequency range.

Development of wideband orthomode transducers for FAST cryogenic receiver system

“…However, the bandwidth of reported dipole OMT is not more than 1.7:1, which does not meet the octave bandwidth requirement of FAST Pband receiver system. In order to broaden the bandwidth of the dipole OMT, a compact wideband bowtie dipole is introduced into a circular waveguide as the feeding structure (Fan et al 2019). The symmetrical structure and center feeding structure of the bowtie dipole OMT increase single mode bandwidth and guarantee no trapped mode generated.…”