兩個新型指向及零點陣列設計－使用九十度耦合器

Abstract

本論文旨在提出新型的架構與設計方式，適當利用九十度耦合器的特性，設計線性回波指向天線陣列與回波與反射波零點天線陣列。 第一章介紹指向天線陣列與零點天線陣列，並於第二章敘述九十度耦合器的基本原理及基本公式推導，並且提出一折疊法，應用九十度耦合器於指向天線陣列和零點天線陣列設計。第三章與第四章則分別利用此方法，設計使用九十度耦合器之線性回波指向天線陣列以及回波與反射波零點天線陣列，並以實驗驗證。 論文第三章主要係分析及製作一線性回波指向天線陣列，使用九十度耦合器以及利用所提出之折疊法設計，並建立一般化電路架構，使其可應用於任意數量天線單元之天線陣列。藉由採用九十度耦合器及折疊法設計之耦合器電路，能使發射天線的輸出訊號之相位差，反相於接收天線的接收訊號之相位差，並且相對於Van-Atta陣列，訊號從輸入埠至平面的耦合器電路，到輸出埠所經過之實際路徑長度皆相同。本章對一般化電路架構，及不理想因素對系統之影響，予以詳細分析，並且製作操作頻率於2.9 GHz之三單元、四單元、以及六單元回波指向天線陣列，藉由量測其輻射場型，驗證所提出之理論，量測結果與理論相吻合。 第四章則敘述使用九十度耦合器及折疊法，設計一可在訊號入射方向及其反射角方向，各產生一零點於其傳輸輻射場型之零點天線陣列。本章首先介紹利用折疊法，設計反射零點天線陣列的原理與實作驗證結果，之後敘述使用折疊法設計一平面耦合器電路，應用於回波與反射波零點天線陣列。相較於使用可適性濾波器理論及數位訊號處理技術，實現零點生成之天線陣列，本章所提出之耦合器電 路由於係利用被動微波元件，因此具有即時響應，在頻率較高場合亦能實現。本章亦提出回波與反射波零點天線陣列的一般化電路架構，使其可應用於任意數量天線單元之天線陣列。考慮電路中各參數對系統之影響，本章亦提出理論的推演與實作考量分析，並製作操作頻率於2.9 GHz的三單元、四單元、五單元、以及六單元回波與反射波零點天線陣列，藉由量測其輻射場型以驗證所提出之理論，且量測結果與理論吻合。

This dissertation presents the study results on two novel designs of retro-directive antenna array and retro- and reflecto-nulling antenna array using 90 hybrids. Chapter 2 introduces the basic theory of operations of the directive and nulling arrays and the basic principles of the folding methods by using 90 hybrids. Based on the folding methods and the theory of operations developed in this chapter, a novel design on retro-directive antenna array is described in Chapter 3 and a novel design of nulling array called “retro- and reflecto-nulling array” is described in Chapter 4. Both the theory and the experiments are studied. Chapter 3 presents a novel approach to design linear passive retro-directive antenna arrays by properly making use of 90 hybrids. For a 90 hybrid, when its direct port and coupled port are terminated with the same reflection coefficient, the phase difference of the reflected signals at the other two ports are reversed to that of the incident signals. This then becomes a phase difference reversal circuit (or a retro-directive circuit) and leads to the design of linear retro-directive antenna arrays using 90 hybrids. In this approach, all signals from the input ports to the output ports of the hybrid circuits inherently have the same path length especially for the planar hybrid circuits. The formulas and a folding method on designing linear retro-directive array circuits with arbitrary element numbers are presented with the measurement results of three-element, four-element, and six-element retro-directive antenna arrays, which are operated at 2.9 GHz. In Chapter 4, a novel approach is developed to design linear passive retro- and reflecto-nulling antenna array which has two nulls occurring at the incident and specular reflection directions without using digital signal processing techniques. At the beginning of this chapter, a four-element reflecto-nulling antenna array is developed to verify the theory of operations of the nulling arrays described in Chapter 2. Then, by the folding method described in Chapter 2, a phase difference reversal circuit developed in Chapter 2 and Chapter 3 can have the phase difference between two adjacent ports of the phase difference reversal circuit be reversed as −Δϕi if the phase difference of the input ports is Δϕi. Thus, the retro- and reflecto-nulling array circuits can be implemented by the array circuits developed in Chapter 2 and Chapter 3 to achieve retro-nulling characteristics and by properly using the phase shifters to achieve reflecto-nulling characteristics. This approach is implemented by a passive circuit with the use of 90 hybrids and phase shifters which are properly connected to the transmitting and receiving antennas. The array then has the retransmitted radiation pattern giving two nulls at the incident direction θi and specular direction −θi as the incident wave angle is at θi. The formulas and a folding method on designing linear retro- and reflecto-nulling array circuits are presented with the measurement results of three-element, four-element, five-element, and six-element retro- and reflecto-nulling antenna arrays operated at 2.9 GHz.