高指向性天線（High-Directivity Antenna）在微波應用的範圍越來越廣，如：汽車雷達（Avoidance Radar）、衛星通訊網路、短距點對點通訊等。又現在的通訊設備中，都朝著小型、輕量、薄型、高頻、低功率與高性能發展，因此要設計出一兼具這些特點的高指向性天線是有其困難度與必需性的。
平面共振式天線相對於微帶陣列天線而言，是一種兼具平面式與高指向性優點的天線，其不需要使用複雜的餽入網路（Feed Network），所以近年來被提出來期望能取代微帶天線陣列，以解決餽入網路中傳輸線的損耗所造成天線增益降低的缺點。但當平面共振式天線的面積縮小時，會產生旁波瓣（Sidelobe）過大的問題，本研究第一個研究主題即在於解決此問題，在平面共振式天線之共振腔的四周圍平面上，分別加上一對完美電牆與一對完美磁牆，如此可成功的使邊長約為兩倍波長的平面共振式天線之旁波瓣位準（Sidelobe Level）降低於-25 dB，其後本研究並成功的使用四分之波長轉換器（Quarter-wave Transformer）結合完美電牆來實現在現實應用中的完美磁牆。
另一個研究主題是可切換式平面共振式天線的設計，本研究提出一個新穎的想法，以PIN二極體來設計可重組態之頻率選擇平面（Reconfigurable Frequency Selective Surface），並以此成功的設計出可切換式之平面共振式天線，使其具有兩種不同的天線性能（指向性），這樣便能將原本需要兩個獨立天線才能達到的性能，如今只需使用單一個天線就能達成，如此可減少天線使用的數量，達到縮減天線使用面積的目的。

Electromagnetic bandgap (EBG) structures and frequency selective surfaces (FSSs) can be employed to control electromagnetic-wave propagation in special directions. They have been widely employed as superstrates of Fabry-Perot (FP) antennas (or called planar resonator antenna) for low-profile directive antennas to as spatial angular filters. Extensive effects have been made in FP antennas for high directivity without complex feed networks like conventional antenna array.
First, A novel approach for reducing sidelobe levels of compact FP antennas is presented in this study. Perfect electrical conductors (PECs) and Perfect magnetic conductors (PMCs) are employed as cavity sidewalls of FP antennas for reducing the sidelobes caused by reducing the antenna size. A quarter-wave transformer along with a PEC is employed to function as a PMC in this study for real applications. The compact FP antennas with high-directivity (~15 dBi) and low sidelobe levels (-25 dB) both in the E- and H-planes are designed. This antenna can be applied to the antennas of short-range vehicular radars.
Then, A novel design of switchable FP antennas for reducing the antenna area is presented in this study. A reconfigurable FSS is employed as a superstrate of a switchable FP antenna. The switchable FP antenna has two performances in one antenna structure switched by bias voltages of PIN diodes. This antenna will be expect to as the antennas of automotive radars that need both high- and low-directivity antennas.

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