Publication:
Design of ultra-high frquency diplexer using quasi-lumped element method

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Date
2012-06-01
Authors
Chew, Soo Siew
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Abstract
In this project, an antenna diplexer using quasi-lumped element method implemented on microstrip transmission line is presented. The antenna diplexer is designed to work in TETRA technology. The base station receiving frequency for TETRA technology is 0.8060 GHz to 0.8210 GHz while for transmitting is 0.8510 GHz to 0.8660 GHz. The center frequencies of 0.8135 GHz and 0.8585 GHz are taken as the operating frequencies of the antenna diplexer. Diplexer is composed of two band pass filter, which are termed as Tx (Transmitting) and Rx (Receiving) filters. The two band pass filters possess a bandwidth of 15 MHz each with frequency separation of 45 MHz. Implementation of low Q microstrip transmission line is a challenge for achieving sufficient isolation between the two filters. Two types of diplexer are designed and tested; one formed by filters with two resonators and the other formed by filters comprise of four resonators. Designs and simulations are done by using CST STUDIO SUITE while Anritsu Network Analyzer is implemented to do the testing and measurement. By comparing the performance of the two designs, diplexer design 2 which formed by filters comprise of four resonators possesses narrower bandwidth and better isolation between two filters. As consequences of achieving narrower bandwidth, the insertion loss and circuit dimension increase.
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