寬頻微波天線饋送技術研究

Abstract

由於通訊系統在高速傳輸的需求下，系統頻寬逐漸走向高頻、寬頻及多頻段。對通訊系統而言，寬頻天線可以利用對數天線或是螺線天線來提升其阻抗頻寬特性，然而對於饋入網路而言，由於必須同時考慮振幅與相位的精準度，因此寬頻操作目前仍是一件困難的工作。 本技術書所規劃內容主要是提出一個系統化的設計觀點來研究寬頻天線饋送網路，在計畫書的第一部份中，我們將先利用系統分析的觀點，配合嚴謹的數學分析建立基本網路架構下每ㄧ積塊之輸出入關係式，因此在串接各積塊後可以做整體之系統分析。 第二部份的工作中，我們將前一部份所規劃的積塊輸出入關係式，利用等效電路來建立該模型，接著以實際之微帶線加以實現。在此部分的工作中，電路分析技術配合電磁全波分析軟體將有助於被動電路的設計工作。最後藉由電路的實際量測來修正電路的原始設計。 在第三部份中，我們將研究利用與傳統傳輸線相反等效電路結構之逆傳輸線特性，並且深入探討其負群速度及寬頻操作的物理機制，由於其負群速度將可以縮小電路之尺寸，因此對於饋入網路之縮小化設計將有極大之助益。此部分的研究工作必須配合第一部份之系統規劃，以及直接應用至第二部份之被動電路設計，方可獲得相輔相成的效果。 本計劃從系統觀點出發，以系統分析來制定每ㄧ被動電路方塊之規格與數學模式，配合被動電路之設計與寬頻機制之研究成果來設計寬頻之系統，此一工作將有助於培養參與計畫之學生系統化工程設計之實務經驗。

The purpose of this proposal is to develop the technology applied in broad-band antenna feeding network. As is well known, due to the rapid increase in the data transmission rate, the wideband or multiple bands communication or radar systems gradually become popular. The wide-band antennas can be achieved by using the log-periodic or spiral antennas. However, to design a feeding network which is able to be operated in a wide bandwidth still is a task remained to be studied in detail. To systematically investigate the wide-band feeding network, this proposal will be divided into three parts; the first one is to develop the system architecture (infra-structure) of the feeding network. Furthermore, the building blocks of the system will be designed and modeled by exact mathematical models. Thus, the system performance including the return and insertion losses of the overall system will be evaluated and optimized. In the second part, we will follow the system specification and mathematical input-output relationship developed in the first part to design the passive circuit, such as broad-band matching circuit, 90 degree hybrid, coupler and band-pass filters. Firstly, the equivalent circuit will be developed to simulate the mathematical function of the corresponding building block. And then the micro-strip lines and junction discontinuities will be employed to synthesize the developed circuit. Moreover, the time-domain full-wave simulation software will be employed to fine-tune the designed circuit before fabricating. Finally, the discrepancy between the measured and simulated results will be carefully investigated to modify the prototype circuit. In the third part, we will focus on the study of broad-band mechanism for the microwave circuit design. Specifically, the NRI (negative refractive index) of a new transmission line containing resonant elements will be studied in this research. Because that the phase and group velocities of the reversed transmission line, having the shunt inductance and serial capacitance in the circuit model, are anti-parallel, such a class of anomalous transmission lines has a negative effective refractive index. This unique property will be studied to apply in the pass circuit design (the second part) to minimize the circuit size and, at the same time, increase the operation bandwidth. This proposal is organized on the perspective of a microwave transmission system. Once the system architecture is determined and evaluated, the passive circuit using micro-strip lines for modeling the input-output relationship of each building block will be designed and fabricated. Incorporated with the broad-band design of the anomalous transmission lines developed in the third part, we could further improve the impedance bandwidth of the passive circuit developed in the previous part of this proposal.