High-selectivity balanced-filter circuits based on coupled lines with open/shorted loaded stubs

Abstract

Two novel balanced-filter circuits based on common coupled lines with open/shorted loaded stubs are proposed in this paper. Two and four transmission zeros near each passband for the differential mode can easily be achieved for two balanced filters. In addition, the common mode can be suppressed from 0 GHz to 3f₀ (where f₀ is the centre frequency of the passband) with insertion loss greater than 25 dB due to the all-stop transmission characteristic of the coupled lines with open/shorted loaded stubs. Two prototypes with 3-dB fractional bandwidths of 12.9% and 13.6% for the differential mode with insertion loss greater than 25 dB (3.5 GHz to 9.1 GHz) are designed and fabricated. Good agreement can be observed between the measured results and theoretical expectations.

Keywords:

• balanced filter
• differential/common mode
• coupled lines
• open/shorted stubs
• bandwidth

Funding

This work was supported by the 2012 Distinguished Young Scientist awarded by the National Natural Science Foundation Committee of China [61225001]; the National Natural Science Foundation of China [6140010914]; Natural Science Foundation of Jiangsu Province [BK20140791]; and the 2014 Zijin Intelligent Programme of Nanjing University of Science and Technology [NJUST2014015].

Additional information

Notes on contributors

Wenjie Feng

Dr Wenjie Feng received his B.Sc. degree from the First Aeronautic College of the Airforce in Xinyang, People's Republic of China in 2008 and his M.Sc. and Ph.D. degrees from the Nanjing University of Science and Technology (NUST) in Nanjing, People's Republic of China in 2010 and 2013, respectively. From November 2009 to February 2010 and March 2013 to September 2013, he was a Research Assistant of the City University of Hong Kong (CityU). From October 2010 to March 2011, he was an exchange student of the Institute of High-Frequency Engineering at the Technische Universität München in Munich, Germany. He is currently a teacher at the NUST. He has authored and co-authored over 50 journal papers and over 20 international conference papers. His research interests include ultra-wideband (UWB) circuits and technologies, substrate integrated components and systems, planar microstrip filters and power dividers as well as LTCC circuits. Dr Feng is a reviewer for IEEE Transactions on Circuits and Systems I, IEEE Transactions on Microwave Theory and Techniques, IEEE Transactions on Industrial Electronics, IEEE Microwave Magazine, and IEEE Microwave and Wireless Components Letters.

Wenquan Che

Prof Wenquan Che received her B.Sc. degree from the East China Institute of Science and Technology in Nanjing, People's Republic of China in 1990, M.Sc. degree from the NUST in Nanjing, People's Republic of China in 1995, and Ph.D. degree from the CityU in 2003. In 1999, she was a Research Assistant of the CityU. From March to September 2002, she was a Visiting Scholar with the Polytechnique de Montréal in Quebec, Canada. She is currently a Professor at the NUST. From 2007 to 2008, she conducted academic research with the Institute of High-Frequency Engineering at the Technische Universität München, in Munich, Germany. During the summers of 2005 to 2006 and 2009 to 2012, she was a Research Fellow and Visiting Professor of the CityU. She has authored and co-authored over 110 journal papers and over 60 international conference papers. She has been a reviewer for IET Microwaves, Antennas and Propagation. Her research interests include electromagnetic computation, planar/coplanar circuits and subsystems in RF/microwave frequency, microwave monolithic integrated circuits (MMICs) and medical applications of microwave technology. Dr Che is a reviewer for IEEE Transactions on Microwave Theory and Techniques, IEEE Transactions on Antennas and Propagation, IEEE Transactions on Industrial Electronics, and IEEE Microwave and Wireless Components Letters. She was the recipient of the 2007 Humboldt Research Fellowship presented by the Alexander von Humboldt Foundation of Germany in 2007, the fifth China Young Female Scientists Award in 2008, and the Distinguished Young Scientist awarded by the National Natural Science Foundation Committee (NSFC) of China in 2012.