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The Scientific World Journal
Volume 2014 (2014), Article ID 671369, 11 pages
Research Article

Reconfigurable Ring Filter with Controllable Frequency Response

Microwave Technology Centre, Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), 40150 Shah Alam, Selangor, Malaysia

Received 11 March 2014; Revised 16 June 2014; Accepted 17 June 2014; Published 8 July 2014

Academic Editor: Run-Cang Sun

Copyright © 2014 Norfishah Ab Wahab 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.


Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2 GHz to 984.4 MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10 GHz to 1.38 GHz spreading over 280 MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity.