A Method for Accurately Characterizing Single Overmoded Circular TM₀₁-TE₁₁ Mode Converter

Abstract

In the case of characterizing waveguide mode converter, the widely applied back-to-back method can only extract two mode converters' joint S-parameters, the accuracy of the far-field radiation pattern method is limited. This paper experimentally demonstrates a method for accurately characterizing single circular TM01-TE11 mode converter, which consists of extracting the asymmetric two-port TM01 and TE11 mode generator test fixtures' S-parameters and de-embedding them from the “TM01 mode generator + TM01-TE11 mode Converter + TE11 mode generator” cascade measurement results. The peak problem occurring in measuring overmoded circular waveguide devices with VNA is analyzed and settled with an offset waveguide based peak-shifting tactic plus the Loess smoothing method. Fairly good agreement between the simulated and finally extracted complex S-parameter matrix of a TM01-TE11 mode converter throughout the device's working frequency span validates the proposed method's merits over traditional methods.

Keywords

• Asymmetric fixture
• de-embedding
• mode generator
• overmoded mode converter
• offset waveguide
• S-parameter