A Study and Fabrication of the λ/4 Coaxial Dielectric Filter and Duplexer

• Main Authors: Yih-Cherng Juang, 莊逸程
• Other Authors: Chung-Chuang Wei ; Cheng-Liang Huang
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/99568264854071875556

碩士 === 國立成功大學 === 電機工程研究所 === 83 === Traditional microwave communication systems were suffering from their huge size and weight since some of the key components were made of metallic waveguide or cavity . Instead of metallic waveguide or cavity , today's microwave devices can be made of ceramics with high dielectric constant , high Q value and good temperature stability . Major advantages that can be seen are the tremendous reduction in the size , the weight ,and the cost . In additions ,ceramic filters provide low insertion loss ,good temperature stability and compact in size which have made the mobile communication possible . Ceramic filters investigated in this work comprise several stages of λ/4- coaxial dielectric resonators supporting the propagation of TEM mode . A proper air gap was constructed to couple electromagnetic energy to next stage between every two neighboring resonators . The frequency response of the filters can be controlled by adjusting the length of the air gap .The duplexer was mainly consisted of transmitting and receiving filters . The (Ba,Sr)O-Sm2O3-TiO2 system was chosen in the fabrication of the filters and duplexer due to its high dielectric constant , high Q value and good temperature stability . In this work , different features of filters were studied . The duplexer was composed of two filters which can fit the frequencies requirement (800MHz-900MHz) of the mobile telephone system . The performance of the duplexer shows more than 50 decibel suppression outside the passband while retaining a 20dB/13MHz shape factor between the transmitter filter(Tx) and receiver filter(Rx) which have the features : (1) Tx: at frequency f=814.3125MHz , S11=-34.406dB , SWR=1.0349 , S21=-2.1421dB , Bandwidth=25MHz . (2) Rx: at frequency f=851.0625MHz , S11=-36.215dB , SWR=1.0267 , S21=-2.3168dB , Bandwidth=25MHz .