研究目的
To design a compact wideband orthomode transducer (OMT) with an octave bandwidth for a cryogenic receiver system in the FAST telescope, minimizing dimension while ensuring good electrical properties.
研究成果
The bowtie dipole OMT achieves a compact size with a length of 300 mm, wide bandwidth of 2.08:1, effective suppression of higher-order modes, and good electrical performance including reflection coefficient below -10 dB and cross-coupling below -30.5 dB. It is suitable for cryogenic applications in radio astronomy, offering advantages in miniaturization and ease of fabrication.
研究不足
The OMT was measured at room temperature, not at the cryogenic operating temperature of 70 K, which may affect performance. The single-mode bandwidth is slightly mismatched to the required band (0.52-1.08 GHz vs. 0.56-1.12 GHz), and further optimization may be needed for exact frequency alignment.
1：Experimental Design and Method Selection:
The OMT was designed using a novel bowtie dipole structure in a circular waveguide to achieve wide bandwidth and suppress higher-order modes. Simulations were performed using Ansys HFSS to analyze transmission coefficients and S-parameters.
2：Sample Selection and Data Sources:
A prototype was manufactured from aluminium using CNC machining.
3：List of Experimental Equipment and Materials:
Aluminium material, CNC machine, Agilent E5071C ENA Series network analyzer, SMA connectors, copper strips, coaxial feeding structures, and a circular waveguide with a radius of 170 mm.
4：Experimental Procedures and Operational Workflow:
The prototype was constructed and measured at room temperature using the network analyzer to obtain reflection coefficients, mutual coupling, and transmission coefficients.
5：Data Analysis Methods:
Data from simulations and measurements were compared; transmission coefficients were derived from back-to-back measurements and calculations for ohmic loss.
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