極化捷變之環狀開槽天線及其應用於自適應天線系統

Abstract

本論文提出一款能在相同的操作頻帶內於線性極化、左手圓極化、右手圓極化之間切換的環狀開槽天線，並將前述天線整合應用在自適應天線陣列系統中。該天線由周長約為一波長的環狀開槽及一對正交的對角線縫隙所組成。沿著對角線縫隙對靠近環狀開槽的位置對稱放置了四個壓控二極體開關，根據不同的開關狀態組合可控制天線的極化狀態，可分別產生線性極化、左手圓極化或是右手圓極化波。而這三種極化狀態可以簡單地經由一組直流電壓去控制，環狀開槽內部被正交對角線縫隙分成四個獨立的扇形區域，藉由分別給予扇形區域正電壓、負電壓或是零電壓，可以讓壓控開關分別操作於短路或開路狀態，以此讓環狀開槽有不同的邊界條件而擾動產生線性極化、左手圓極化和右手圓極化三種不同的極化狀態，且三種不同的極化狀態具有接近的共振頻率及高度重疊的操作頻寬。此外，所提出的天線在陣列架構中具有更小的互耦合，因此設計時可縮短相鄰天線單元之間距，以達到更大角度的波束掃描和更低的旁波束位準。最後，將所提出的天線架構整合至本實驗室先前提出的自適應天線陣列系統中，並以實驗驗證系統之效能。

In this thesis, we first propose a polarization-agile slot ring antenna that is capable of switching among linear polarization (LP), left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) while operating within the same frequency range and then use the antenna structure as array element in a self-adaptive antenna array system. The proposed antenna consists of a microstrip-line-fed one-wavelength slot ring and a pair of orthogonal diagonal silts etched inside the slot ring. By symmetrically placing four PIN diodes across the diagonal slits near the junctions between the slot ring and slits and by adjusting the associated control DC voltages, the polarization state of the proposed antenna can switch among LP, RHCP, and LHCP. The three polarization states can be controlled simply by a set of DC voltages. The inner circular metallic area of the slot ring is cut into four independent fan-shaped regions by the orthogonal diagonal slits. By providing the four fan-shaped sectors with positive, negative, or zero voltages, the four PIN diodes can be turned on or off, respectively. In this way, the PIN diodes impose different boundary conditions to the slot ring radiator, and the perturbation thus formed results in LP, LHCP, or RHCP radiation. For different polarization states, the resonant frequency of the proposed antenna remains almost the same, and the operational frequency range overlaps as well. Besides, because the mutual coupling of the proposed antenna, when arranged in an array, is relatively low, the inter-element spacing can be properly reduced to achieve a wider angular range of beam scanning and a lower side-lobe level. Lastly, the proposed antenna is used as array element and integrated into the self-adaptive antenna array system previously proposed by our laboratory. The performance of the modified system is verified experimentally and also presented in the thesis.