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 TE₀₁mode converter design. The structure consists of 16-dividing waveguide network and TE₀₁mode 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.