Varactor-tuned coupled resonator front-end bandpass filters for cognitive radio applications

Abstract

The design, implementation and measurement results of varactor-tuned, three coupled resonator, bandpass filters for cognitive radio applications are described. Two distinct filters, one covering 176 MHz-216 MHz and the other covering 476 MHz-698 MHz is described. The filters were implemented using commercially available surface mount components on an FR-4 printed circuit board. The purpose of the bandpass filters is to provide selectivity in the front-end and provide protection from interferers. The two filters improved the intermodulation rejection of the receiver by 24 dB and 27 dB respectively.