Analysis and Design of Branch-Line Couplers with Miniaturization and Multi-band

• Main Authors: Chen, Ming-Guang, 陳明廣
• Other Authors: Tang, Ching-Wen
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/14260615583264440483

博士 === 國立中正大學 === 電機工程研究所 === 99 === This dissertation presents the investigating of microwave branch-line couplers with miniaturization and multiple passbands. With the approach of adding multiple open stubs in four branches, the size of the quarter-wavelength transmission line in the branch-line coupler can be reduced greatly. Moreover, this is the first investigation upon the predetermined operating bandwidth and shrinkage rate of circuit area before fabricate the microstrip branch-line couplers. It concludes that open stubs with low impedance perform better than those with high impedance; moreover, the more open stubs with low impedance utilized, the broader the bandwidth will be. However, the increasing the shrinkage rate of circuit size will result a smaller operating bandwidth. To avoid the drawback of smaller operating bandwidth, the dual transmission lines are proposed to replace conventional quarter-wavelength transmission lines for a compact microstrip branch-line coupler in the second study. With the assistance of the dual transmission lines, a compact planar branch-line coupler has been developed at the operating frequency as 2.4 GHz. The size reduction rate is 63.9% from the conventional branch-line coupler to the proposed one. The third study is the microstrip branch-line coupler with multiple passbands. In order to obtain multiple passbands, open stubs are added to the conventional branch-line coupler’s ports; in addition, these open stubs’ impedance and electrical length need to be properly chosen. The design theory and analysis of compact and multi-band branch-line couplers are introduced. Measured results of fabricated examples match well with simulation; therefore, the feasibility of the proposed structures have been validated. Moreover, the proposed couplers can be easily fabricated on the printed circuit board without any lumped element.