| Summary: | 碩士 === 國立臺灣海洋大學 === 電機工程學系 === 101 === In this thesis, the design of an ultra broadband standard log-periodic dipole antenna (LPDA) is considered. The frequency-independent characteristics of LPDA enabled the realization of wide bandwidth with stable gain and desired radiation pattern. Based on the operation principles of LPDA, several design consideration for LPDAs have been fabricated on printed circuit board. The first design operated as endfire array which required a larger space requirement for practical applications. To downsize the effective space requirement, we have modified our design for the planar LPDA to that of the broadside array. However, the planar broadside array LPDA has inherent difficulty in achieving good impedance matching. To solve this problem, we have implemented a three-dimensional microstrip line impedance converter to improve the impedance match. Nevertheless, the process can be quite complicated and the 3D feed generally resulted in a large effective volume for practical application. Finally, we have devised a simple modified LPDA such that a planar microstrip line impedance converter can be incorporated to improve the impedance matching of the LPDA. Our modified planar LPDA can operate satisfactorily within the bandwidth from 1.7 GHz to 6.5 GHz with return loss of below -10 dB and a maximum gain of 6.2 dBi.
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