Gap Influence and Mode Converter Design for Non-destructive Complex Permittivity Measurement Using Circular TE01-mode Open-end Waveguide

This paper proposes a non-destructive complex permittivity measurement method using circular TE01 mode. First, we discuss on the influence of gap by comparing conventional coaxial probe method and circular TE01 mode method that we propose. They are quantitatively compared based on the analysis with the help of EM-field simulator. It is shown that the proposed method is about 10 times insensitive to the air gap. Next, we show the actual TE(01)mode converter design. The structure consists of 16-dividing waveguide network and TE01 mode excitation part. Two models are designed. First, X-band model is designed and manufactured. Whole structure analysis by the simulator result agreed well with measured S11 parameter. Next, K-band model is designed with improved reflection characteristics. Whole structure analysis showed that the relative bandwidth for reflection below -20dB achieved 37.8% within K-band frequencies.