Tunable band-stop filter with combined Right/Left-Handed Transmission Line

In this paper, a tunable band-stop filter based on right-handed transmission lines (RHTLs) of low-pass characteristics and left-handed transmission lines (LHTLs) of high-pass characteristics are developed. This filter consists of a parallel connection of the RHTLs and LHTLs. Varactor diodes and chip inductors are used to make the unit cells of RHTLs and LHTLs. The cut-off point of the RHTLs becomes the lower cutoff frequency of the band-stop filter and the LHTL becomes the upper cut-off frequency. Therefore, upper and lower cut-off frequencies of the proposed band-stop filter can be controlled by the voltages of the varactor diodes, individually, and it is easy to change the center frequency and the bandwidth. The measured results of the tunable band-stop filter show a minimum bandwidth at 85.8% and a maximum at 133% from a center frequency of 600 MHz. While the minimum insertion losses at pass-band are -0.9 dB.