A tunable wideband microstrip bandstop filter based on liquid crystal materials

A compact liquid crystal (LC) based tunable wideband microstrip bandstop filter (BSF) is presented in this paper. To realize a compact size and wide stopband bandwidth, a double-stub bending structure was designed. The BSF stopbands can be tuned by applying a voltage between 0-20 V to regulate the LC dielectric permittivity. A tunability >7% and 3dB bandwidth > 3 GHz and 2.5 GHz for the first and second stopbands respectively were achieved. The rejection level was higher than 41 dB. Such a LC based BSF device with a high tunability, wide stopband bandwidth, low driving voltage and compact size are useful in a wide range of applications.