以隙環共振器實現微小化天線設計

Abstract

本論文中介紹了隙環共振器的基本工作原理，並提出簡單的近似公式來估算其共振頻率。據此，我們提出兩款微小化天線設計，分別以金屬隙環共振器及互補式隙環共振器來實現。第一款係利用小金屬圓環，耦合饋入金屬隙環共振器，為了進一步抑制金屬接地面對天線效能的影響，第二款設計則是以互補式隙環共振器實現。實際上，這兩款天線均能有效匹配至50 Ω，且其尺寸均約為(λ_0⁄20)×(λ_0⁄20)。 為了公平比較不同縮小化程度的天線，我們採用天線的實際品質因子(Q值)與其以理論算出之最小可能的品質因子(Chu limit)之比值來比較不同的微小化天線。為此，我們亦嘗試整理過去有關Chu limit的研究結果，從天線尺寸對於天線效能的限制以及天線的品質因子與頻寬之間的關係等。為了理論推導的一致性，我們統一使用了傳統品質因子的定義。最後，我們利用理論所得到的頻寬限制，比較了兩款參考文獻中的微小化天線與我們的設計。同時，也討論這些限制的適用範圍，並探討理論中的假設可能的物理意義，最後提出可能的方向來趨近或突破這些效能上的限制，提出未來可能的研究方向。

This paper proposes two antenna designs of planar split ring resonator (SRR) structure fed by coplanar grounded waveguide. In the first design, we use a small loop to feed the SRR structure antenna, so the bandwidth and efficiency are improved from the precious design. In order to eliminate ground size effect, we propose another design, using a slot to present SRR structure. Both designs were designed to match to 50 ohms, and the geometric dimensions are both at about (1⁄20) λ_0×(1⁄20) λ_0. To compare with well-proposed designs, we use the quality factor and the Chu-limit to analyze various electrically small antennas which work on separate frequency; therefore, we obtain the advantage of our design comparing to the well-proposed designs. Since various definitions of Quality factor and various derivations of Chu-limit under different assumptions have been considered at previous works, we direction different researches, and unify the definition on quality factor to their results. Moreover, by summarizing these results, we illustrate the physical meaning of these hypotheses, thus some novel perspectives on designing electrically small antenna are proposed.