新型多頻印刷偶極天線與縮小化印刷摺疊偶極天線設計

Abstract

本論文的前半部分提出一全新架構之多頻印刷偶極天線設計，不同於傳統偶極天線由中間饋入訊號的方式，透過印刷偶極天線結合改良之環形微帶線分合波器，實現由兩端饋入訊號之新型態偶極天線架構。由於訊號在環形微帶線分合波器的兩輸出端埠，會隨著操作在不同的頻段而有不同的相位差與振幅比，平衡與非平衡的訊號將進而形成不同的共振模態與相對等效輻射路徑，且環形微帶線分合波器在輸入端埠具有超過80%的10dB反射損耗頻寬。本論文即結合以上特性，藉由巧妙的整合與設計，成功實現印刷偶極天線多頻段、寬頻帶的操作。

本論文的後半部分提出一天線縮小化新方法。透過加入摺疊偶極天線適當大小形狀之對稱性環形寄生金屬，環形寄生金屬上會產生感應之映像電流延長輻射路徑，並形成環形天線模態共振輻射同時會提供自身之電阻與摺疊偶極天線串聯。在此過程結構本身帶有的封閉電流迴路將產生電感性電抗補償低頻時電容性的偶極天線，成功達到大幅降低天線共振頻率之目標。以共振頻率為1.4GHz之單邊繞折印刷摺疊偶極天線設計作為中心根基天線，結合環形寄生金屬後，共振頻率可降至0.87GHz且仍維持良好的輻射特性。本論文研究中，將針對寄生環形金屬對印刷折疊偶極天線的影響，以及造成降頻的物理機制與原理，作深入的探討。

Multi-band printed dipole antennas with brand-new structure are presented in first part of this thesis. Unlike traditional dipole antenna fed from the center, a printed dipole antenna integrated with modified microstrip ring hybrid can realize a novel model of dipole antenna which is fed from end to end. Because the phase difference and magnitude ratio of signals from two output ports of microstrip ring hybrid vary from frequency to frequency, balanced and unbalanced signals will be produced to form different resonant mode and relative effective radiaton path. Furthermore, there is more then 80% -10dB return loss bandwidth in input signal of microstrip ring hybrid. This thesis combines above aspects with sophisticated integration and design to achieves a target of multi-band and wideband operation of printed dipole antenna successfully.

A new method of antenna miniaturization is presented in second part of this thesis. Adding symmetric annular parasitic conductor of appropriate shape and size to folded dipole, image current will be induced in annular parasitic conductor while the total radiation length will be increased. Moreover, annular parasitic conductor with induced current working as loop antenna will be resonated to radiate and provide its resistance in series with folded dipole simultaneously. Among above process, the inductive reactance will be produced by the structure carrying closed current loop to compensate capacitive dipole antenna at lower frequency, and it eventually attains the objective of bringing about large amount of drop in resonant frequency of proposed antenna successfully. The design of 1.4GHz printed folded dipole antenna with one side meandering is taken as elementary antenna. After integrating elementary antenna with annular parasitic conductor, the resonant frequency can drop from 1.4GHz to 0.87GHz, and the good radiation property still be maintained. The effect of annular parasitic conductor toward printed folded dipole antenna and the physical mechanism and principle which cause frequency drop will be further discussed in our research of this thesis.