A compact tunable bandpass filter with high selectivity and low insertion loss using novel CRLH cell

摘要

This paper presents the realization of a tunable bandpass filter with high selectivity and low insertion loss using one tunable composite right/left-handed (CRLH) cell. The tunable CRLH cell is proposed with varactor diodes loaded both on series and shut circuits. Two shut circuits are designed to form the needed paralleled C_R and L_L, by which two transmission zeros beside the passband are obtained at the same time. Each varactor diode is shunted by a lumped capacitor for lower insertion loss. The filter is tuned by only one DC bias, which results in easily control and compact size. The measured results agree well with the simulated results, and a tunable range of the center frequency from 1.75 to 2.25 GHz is achieved in measurement with the insertion loss less than 2.5 dB.