以多模態波導設計陷波濾波器與吸收器之研究

本篇論文將利用多模態波導之特殊幾何結構，將高階模態侷限在內部，進而形成等效的共振腔，藉由兩種模態之間的干涉行為來設計陷波濾波器與吸收器。不同於一般矩形波導只能傳遞主模態TE10，多模態波導允許其他高階模態同時為傳播模態，因此在K頻段(18 GHz - 26.5 GHz)的頻率範圍內選擇TE10模態與TE30模態進行模擬與實驗。本篇論文設計出一種曲線式口徑轉換的多模態波導，其幾何形狀為對稱結構，兩端口徑寬度由標準尺寸10.668 mm向中間逐漸增加至22.86 mm，並在中間口徑最寬的區域填充部分介電質以激發TE30模態；由於截止頻率的特性，隨著口徑寬度縮減至特定寬度時，TE30模態將從傳播模態轉變為截止模態，進而在波導內部形成等效的共振腔。若以此結構作為雙埠系統，在共振頻率時的頻率響應將顯示為高反射，可以用來設計陷波濾波器；若作為單埠系統，在共振頻率時的頻率響應將顯示為高吸收，則可以用來設計吸收器。透過時域耦合模態理論可以清楚地瞭解並解釋系統在共振時，兩種模態疊加之後的干涉行為，並透過改變介電質的介電係數與尺寸，得到不同的頻率響應。本論文使用電磁模擬軟體HFSS並配合時域耦合模態理論來找出最佳化的結果，最後實際製作成品進行量測，並與模擬結果做驗證。此外，為了使模擬更能符合實驗條件，我們將自行量測介電質的介電係數與正切損耗(loss tangent)，使之作為模擬軟體之參數設定。

關鍵字

多模態波導；陷波濾波器；吸收器；時域耦合模態理論；介電係數量測

並列摘要

An overmoded waveguide is presented through changing the dimension of width. We put a dielectric in middle of the waveguide in order to excite higher order modes. Because of higher order modes can only exist in the wider dimension of width, effectively form a cavity in the waveguide. Then we design notch filters and absorbers by the interference conditions of two modes composition. We choose TE10 mode and TE30 mode as two operating modes in K-band. At the beginning of this work, we simulate the frequency responds of different structures by the simulation program “HFSS”, then put the design structure into the real waveguide for testing. Finally we compare the differences between the simulation results and measurement data and take the temporal coupled-mode theory into consideration for further optimization of the design. We also measure the permittivity and loss tangent of the dielectric in rectangular waveguide for simulation settings.

並列關鍵字

Overmoded waveguide ； notch filter ； absorber ； temporal coupled-mode theory ； complex permittivity measurement

參考文獻

[2] G. A. Ediss, “Measurements and Simulations of Overmoded Waveguide Components at 70-118 GHz, 220-330 GHz and 610-720 GHz.” 14th International Symposium on Space Terahertz Technology.

[3] Christopher D. Nantista and Sami G. Tantawi, “Overmoded Rectangular Waveguide Components for a Multi-Moded RF Power Distribution System.” Proceeding of EPAC 2000, Vienna, Austria.

[8] Deepak K. Ghodgaonkar, Vasundara V. Varadan and Vijay K. Varadan, “A Free-Space Method for Measurement of Dielectric Constants and Loss Tangents at Microwave Frequencies.” IEEE Trans. Instrum. Meas., vol. 37, no. 3, Jun. 1989.

[9] Atsuhiro Nishikata, “A Swept-Frequency Measurement of Complex Permittivity and Complex Permeability of a Columnar Specimen Inserted in a Rectangular Waveguide.” IEEE Trans. Microw. Theory Tech., vol. 55, no. 7, Jul. 2007.

[10] Hayato Miyagawa, Kikuo Wakino, Yu-De Lin and Toshihide Kitazawa, “Simultaneous Determination of Complex Permittivity and Permeability of Columnar Materials With Arbitrarily Shaped Cross Section.” IEEE Trans. Microw. Theory Tech., vol. 57, no. 9, Sep. 2009.

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以多模態波導設計陷波濾波器與吸收器之研究

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