運用序列轉動饋入法之圓極化背接金屬共平面波導槽孔天線陣列

Abstract

背接金屬共平面波導以主模(共平面波導模態)傳遞電磁波，在任何頻率下皆會激發表面波往兩側傳遞，我們運用此特性設計使其成為良好傳輸線。 利用全波分析，得知該表面波以某一角度偏離主軸傳遞。在已知偏離角度下，沿該角度射線每隔一波長蝕刻一矩形槽孔，使每個槽孔被等相位地激發。當矩形槽孔長邊遠大於寬邊，並約等於二分之ㄧ波長(共振長度)時，電磁波便能有效地朝空氣輻射能量形成天線，最後可得一集中的邊射輻射場型。 現代衛星通訊系統運用圓極化去達到最佳化極化效率。我們將線性極化的天線運用序列轉動饋入法去達成圓極化效果。直播衛星收發天線運用在12 GHz的頻段，要求高增益與高效率。本論文研究遂將此圓極化天線的操作頻率設計在該頻段上，最後可得24.84 dBiC的輻射增益以及330 MHz的圓極化軸比3 dB頻寬。

Conductor-backed coplanar waveguide (CBCPW) exists two dominant modes including CPW and parallel plate modes with no cutoff frequency. The latter one causes the power leakage into transverse direction. We use the characteristic to design it as a good transmission line. Implementing the full wave analysis (Spectral Domain Approach) on the CBCPW structure, we can acquire the information that the surface wave propagates along a particular angle relative to the main CPW line. So, we etch rectangular slots along the angle on the two side ground planes. Because the slots are separated one guided wavelength, they are excited in the same phase. If the long dimension of the slot is significantly longer than the wide one and approximately equals to a half of guided wavelength, the slots fed by CBCPW can radiate power efficiently. Finally, we derive a broadside radiation pattern. Modern satellite communication systems use circular polarization (CP) to maximize the polarization efficiency. We use the sequential rotation feeding method to produce circular polarization antennas with linearly polarized elements. The antenna for direct broadcast from satellites (DBS) is operated at 12 GHz and asked for high gain and efficiency. We design our antenna to operate at this frequency. Finally, we have the measured radiation pattern with 24.84 dBiC and the measured axial ratio 3 dB bandwidth with 330 MHz.