Design of Novel Multi-Band Printed Dipole Antennas and Miniaturized Printed Folded Dipole Antennas

• Main Author: 鄭力元
• Other Authors: 陳富強
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/49105943661162720962

碩士 === 國立交通大學 === 電信工程系所 === 97 === 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.