FULLY ADAPTABLE BAND-STOP FILTER USING VARACTOR DIODES

In this article a reconfigurable band-stop filter able to reconfigure center frequency, bandwidth, and selectivity for fine tuning applications is demonstrated, device topology discussion and implementation details are given, and followed by discussion on simulations and measurements.The reconfigurable filter topology has four poles and a quasi-elliptic band-stop filter response. The device is tuned by varactor diodes placed at different locations on the filter; varactors are voltage controlled in pairs due to filter symmetry for center frequency and bandwidth control. An additional varactor is placed on a crossing line to move a pair of transmission zeros, closer or farther to the filter center frequency, which tunes filter selectivity. Simulations show a tuneable center frequency range from 1.42 to 1.48 GHz, a tuneable fractional bandwidth range from 9.46 to 12.96%, and a tuneable selectivity range from 0.53 to 0.65 dB/MHz. Measurements show a tuneable center frequency range from 1.37 to 1.43 GHz, a tuneable fractional bandwidth range from 11.31 to 15.93%, and a selectivity tuning range from 0.37 to 0.40 dB/MHz. Simulations and measurements are in good agreement. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 554–558, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/mop.24969

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