4-Pole Tunable Absorptive Bandstop Filters Using Folded Coupled-Lines With an Inductor

The ever-growing field of wireless communication requires efficient radio frequency transceivers with tunable absorptive bandstop filters that can prevent the interference out-of-band and reflected signals. This paper presents 4-pole using folded coupled-lines an inductor. A filter transfer function is achieved to obtain coupling diagram 45° electrical-length transmission-line source/load coupling. folded-loaded inductor are proposed control for required coefficients based on functions. quality factor extracted through accomplished a distributed resonator loaded asymmetrical varactors without auxiliary circuits, such as impedance-matching network. Two types were designed built substrate ε r = 3.42 h 30 mil. center tuning was performed silicon varactors. first shows return loss 16.2–38 dB rejection level 41–48 in range 0.83–1.09 GHz. second results measured 14–34 40.1–51 at 1.16–1.47 high attenuation reflectionless responses which have applications cognitive radios carrier aggregation systems.