本論文提出應用於Ka頻段系統之圓極化背腔式孔徑天線設計。天線由一個孔徑天線及一個背腔反射板組成，由於孔徑天線具有雙向輻射的特性，因此在天線下方放置背腔反射板來抑制向下輻射與提高天線增益。為了避免天線在傳輸或接收電磁波的過程中受到多重反射干擾，而圓極化天線可以減輕這方面的問題並提高傳輸訊號的品質與穩定度，本設計藉由調整L型饋入結構的長度與寬度來改變相位差及大小進而產生圓極化的效果，透過加入殘段、步階結構與改變背腔形狀，可以有效的拓展阻抗頻寬及軸比頻寬。 天線的設計是使用台灣半導體研究中心提供之RO4003高頻兩層板材製作，天線的背腔厚度為0.125 λ0 (λ0為26.5 GHz的自由空間波長)，天線的量測結果顯示阻抗頻寬為55.07% (22.75-40.04 GHz)，軸比頻寬為20.16% (26-31.38 GHz)及2.19%(35.56-36.35 GHz)，所提出的天線呈現右手圓極化，且最大增益為8.26 dBi。 ;Designs of circularly polarized cavity-backed aperture antenna for Ka-band applications are proposed in the thesis. The proposed antenna consists of a cavity-backed aperture. The aperture has the characteristics of bidirectional radiation, so that a cavity-backed reflector is placed under the aperture to suppress downward radiation and increase upward antenna gain. In order to prevent the antenna form being interfered by multiple reflections when transmitting or receiving electromagnetic waves, the circularly polarized antenna can improve the quality and stability of the transmission signal. In this design, the phase difference and size are changed by adjusting length and width of the L-shaped feed structure to produce the effect of circular polarization. By adding stubs, stair-shape structures and changing the shape of the cavity, the impedance bandwidth and axial ratio bandwidth of antenna can be effectively enhanced. The proposed antenna is made of RO4003 high-frequency two-layer board provided by Taiwan Semiconductor Research Insitute. The cavity thickness of the antenna is 0.125λ0 (λ0 is the free space wavelength at 26.5 GHz). Measured results of the antenna show that the impedance bandwidth is 55.07% (22.75-40.04 GHz), axial ratio bandwidth is 20.16% (26-31.38 GHz) and 2.19%(35.56-36.35 GHz). The proposed antenna exhibits right-handed circular polarization with a peak gain of 8.26 dBi.
