以連通柱實現超微小化頻率選擇面之設計方法

Abstract

頻率選擇面(Frequency Selective Surface, FSS)為一種空間濾波器，經過適當設計的頻率選擇面可以對特定頻帶內的電磁波產生全反射或全穿透的效應。本文提出一種新穎的頻率選擇面微小化設計方法，用以解決系統封裝時所造成的雜訊輻射干擾。由於電磁及射頻干擾問題易發於高整合度的系統封裝，為了達成需求之系統的電氣特性，可用於系統封裝之微小化的頻率選擇面將是設計者的共同目標。透過本文所提出的微小化設計方法，可將頻率選擇面的尺寸大幅縮小，進而大幅提升頻率選擇面於系統級封裝上的應用。該方法跳脫原先只能在二維(X-Y平面)電路印刷版上設計元件限制，改以在第三維度(Z軸)引入連通柱(via)共設計的方法，此方法將比傳統二維頻率選擇面(Two-dimensional FSS, 2-D FSS)多一個設計參數的自由度，透過此方法設計出的頻率選擇面稱為2.5-D FSS。藉由本文提出的最佳化設計方法，此概念可被實現於單層或多層的印刷電路板中，其電氣尺寸僅有0.04 λg × 0.04 λg，更是所有頻率選擇面中尺寸最小的。 首先本文提出以在Z方向增加頻率選擇面元件的等效電感效應的方式來實現2.5維之超微小化結構，並透過完整的電路分析與全波模擬相互驗證後，將該元件實作於四層板上進行量測，量測所得之頻率響應圖有良好特性。為了更進一步將低製作成本，改利用文中提及的微小化方法來增加頻率選擇面元件的等效電容效應，此元件則可直接實現於單層印刷電路板上，量測所得之頻率響應圖亦有良好特性。上述分別透過電感或電容增強效應的元件之電路架構均被完整的分析，並詳述其設計流程。 有別於頻率選擇面只能與全反射或全穿透的濾波形式抑制雜訊干擾，頻率選擇面吸波材(absorber)則可以直接吸收雜訊，本文所提供之方法亦可以使用於微小化吸波材的設計，對於該方法所實現之吸波材亦均有完整電路分析與實驗結果相互驗證。值得注意的是，本文是第一個提出使用第三維度上的連通柱之設計方法來解決頻率選擇面微小化的問題

One novel 2.5-dimensional ultraminiaturized element and two methodologies are proposed in this dissertation for addressing the problem: as applying FSSs in a limited region, including a sufficient number of resonant-type elements to enable the FSS to act as an infinite FSS featuring low sensitivity to incident waves is difficult in practical application. At first, a new 2.5-dimensional ultraminiaturized element on a cost-effective printed circuit board to build a frequency selective surface (FSS). The proposed element consists of two main parts: a planar tapered meandering line (PTML) and a vertical via-based meandering line (VVML). Compared with previous published two-dimensional miniaturized elements, the proposed element is smaller (only 3.3% of the free space wavelength at the resonant frequency) and exhibits high resonant stability at various polarizations and incidence angles (only 0.4% deviation at the resonant frequency when the incident angle is as great as 75°). Second, a novel methodology is proposed for minimizing the size of the periodic element and tuning the resonant frequency of a single-layered frequency selective surface (FSS). Vertical vias are introduced to the FSS design in the methodology. Through the proposed methodology, users can easily vary the resonant frequency of the considered via-inserted FSS (VI-FSS), adding only some additional vias and without having to modify the original element pattern. For demonstrating the capability of the via-based methodology further, it was applied to two advanced applications: two miniaturized-element FSSs and an FSS absorber. Thus, a significant performance improvement in these applications reconfirmed the capability of the proposed methodology. Finally, another novel methodology is proposed for minimizing the size and thickness of FSS absorber element. Vertical vias are introduced to the FSS absorber design for the first time. The methodology can also be applied to dual band FSS absorber design. A novel via-inserted element is used to illustrate how to apply the methodology to dual band FSS absorber design. A prototype of the miniaturized-element and miniaturized-thickness dual absorber was created and examined. The results show that there is good consistency among full wave simulation, circuit model and measurement. It is worth noting that it is the first dissertation to employ inserted-via design concept for achieving FSS and FSS absorber minimization.