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Mathematical Problems in Engineering
Volume 2014, Article ID 679538, 6 pages
http://dx.doi.org/10.1155/2014/679538
Research Article

Investigation of Compact Balun-Bandpass Filter Using Folded Open-Loop Ring Resonators and Microstrip Lines

1Institute of Microelectronics and Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan
2Institute of Microelectronics and Department of Electrical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 701, Taiwan
3Department of Electrical Engineering, National University of Kaohsiung, Kaohsiung 811, Taiwan
4Department of Electronic Engineering, Southern Taiwan University, Tainan 710, Taiwan
5Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 811, Taiwan

Received 2 May 2014; Accepted 7 June 2014; Published 1 July 2014

Academic Editor: Teen-Hang Meen

Copyright © 2014 Chia-Mao Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A balun-bandpass filter was proposed by using two folded open-loop ring resonators (OLRRs) to couple three microstrip lines. By tuning the size of the OLRR, the operating frequency of the balun-bandpass filter could be tuned to the needed value. By tuning the size of open stub at the end of microstrip lines, the balanced impedance of the balun-bandpass filter could also be tuned. The fabricated balun-bandpass filter had a wide bandwidth and a low insertion loss at center frequency of the passband. The balun-bandpass filter presented an excellent in-band balanced performance with common-mode rejection ratio more than 20 dB in the passbands. An advanced design methodology had been adopted based on EM simulation for making these designed parameters of OLRRs and microstrip lines. Good correlation was seen between simulation and measurement, and the result was that first run pass had been achieved in the majority of our designs.