本論文提出三種具備帶通特性的頻率選擇面設計，包含兩個被動式頻率選擇面，以及一個基於液晶材料的可調頻率主動式頻率選擇面。其中，第一個被動式頻率選擇面設計是藉由偶合兩層金屬層分別是十字狹縫與矩形網格貼片來達到高選擇性，頻寬介於29GHz~30.3GHz，約是中心頻率29.6GHz的4.4%，並透過簡單且對稱的圖案設計來達到極化不敏感特性，可接受的電磁波入射角度也達到75度，同時僅有0.1%(TE)與0.4%(TM)的偏差量，代表其具備高角度穩定性。第二個被動式頻率選擇面則是透過兩層迴圈狹縫振盪器與正方形的偶合狹縫的交互作用，產生兩個傳輸極點，達到平頂的傳輸特性，其頻寬是11.98~12.75GHz，是中心頻率12.37GHz的6.2%，此外，高角度穩定的特性使其在0度~60度的入射角量測中僅有最大0.2%(TE)與0.4%(TM)的頻率偏差量。第三個是主動式頻率選擇面，其頻寬是26.09~33.32GHz，透過在結構中加入向列型液晶材料，通過電壓控制改變液晶材料的介電常數來達到調整工作頻率的特性，此設計使用介電常數變化量0.45的Merck E7，在模擬中達到5.06%的頻率調整量，並透過實驗驗證模擬的正確性，在量測結果中顯示在正入射時最大的工作頻率調整量約是4.8%，偏壓前的中心頻率是30.04GHz，偏壓後是28.56 GHz，與模擬的頻率偏差量分別只有4.73%與4.94%，主要是由製作過程中的公差，但整體而言量測與模擬的結果吻合。

In this thesis, experimental research of hybrid frequency selective surfaces (FSS) based on metamaterials and liquid crystal materials has been conducted. Three different case designs of FSS either through an active or a passive configuration were proposed and experimentally investigated.
In the first case, a novel design of a narrow band-pass FSS based on the utilization of the coupled method, which resonates at Ka-band frequencies between 29 GHz and 30.3GHz, is proposed and experimentally evaluated. High selectivity was achieved, by coupling two metallic layers, in which they were based on the structure of a cross aperture and a rectangle grid patch respectively. The simple symmetric patterns used in the proposed work have also made the FSS independent of polarization properties. Moreover, high angular stability was also achieved since for electromagnetic wave (EM) wave incident at degrees from 0° to 75°, the frequency deviations were only 0.1% and 0.4% for TE and TM polarizations respectively. For performance evaluation, an experimental FSS prototype has fabricated by a double-sided PCB, which was composed of 50 × 50 unit cells in a dimension of 18cm×18cm. A Keysight N5227A PNA network analyzer and two horn antennas in a chamber were set up to conduct the performance measurement. The experimental measurement results have shown a good agreement with numerical simulations.
In the second case, an experimental investigation of an ultrathin narrowband FSS with polarization-insensitivity and high angular stability at X-band is reported. A roll-off and narrow passband were realized by coupling top and bottom two square loop aperture metallic layers and a middle square aperture metallic layer respectively. The numerical simulations were verified through an FSS prototype that has fabricated through the normal PCB technology. The prototype was composed of 50 × 33 unit cells in a dimension of 40 cm × 26.4 cm, and the total thickness is 0.025λ. From the experimental results, the center frequency of the FSS prototype had been measured as 12.23 GHz and the 3-dB bandwidth is around 6.1% of the center frequency. Moreover, a maximum frequency deviation of 0.4 % with incident angles from 0° to 60° had been measured. These experimental results have further verified the correctness of the numerical simulations.
In the third case, a novel design of reconfigurable FSS using nematic liquid crystal (LC) materials is reported. The LC-FSS resonates at Ka-band frequencies to provide a bandpass nature. The reconfigurability was achieved by altering the dielectric anisotropy of LC materials. This study used a Merck-E7 LC material with dielectric tunability of nearly 0.45 to study the resonance characteristics. Full-wave simulations have achieved a frequency tunability range of 5.06%. An LC-FSS prototype of 7cm×7cm in size was fabricated for experimental evaluation, consisting of 25 × 25 unit cells. The measurement results show that a maximum frequency tunability close to 4.8% has been achieved for a normally incident illumination of electromagnetic waves. Moreover, the maximum frequency deviations were only 4.73% and 4.94% with/without a bias voltage to shift the center frequency. These experimental results have precisely verified the numerical simulations despite the frequency deviations resulting from the fabrication tolerances.

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