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International Journal of Antennas and Propagation
Volume 2015, Article ID 762504, 6 pages
Research Article

High Selectivity Dual-Band Bandpass Filter with Tunable Lower Passband

School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China

Received 31 December 2014; Accepted 28 February 2015

Academic Editor: Dimitrios Sounas

Copyright © 2015 Wei-Qiang Pan 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.


This paper presents a novel method to design dual-band bandpass filters with tunable lower passband and fixed upper passband. It utilizes a trimode resonator with three controllable resonant modes. Discriminating coupling is used to suppress the unwanted mode to avoid the interference. Varactors are utilized to realize tunable responses. The bandwidth of the two bands can be controlled individually. Transmission zeros are generated near the passband edges, resulting in high selectivity. For demonstration, a tunable bandpass filter is implemented. Good agreement between the prediction and measurement validates the proposed method.