Substrate-integrated octave-tunable combline bandstop filter with surface mount varactors

This paper presents an octave-tunable two-pole bandstop filter with tuning range of 0.56-1.18 GHz (2.1:1 tuning ratio). The bandstop filter is designed with two highly loaded combline resonators with surface mounted solid state varactors. Theoretical analysis and modeling along with full wave simulation is presented in agreement with measured data. The measured peak attenuation in the stopband is approximately 27 dB at 1.18 GHz and is approximately 7 dB at 0.56 GHz. However, a minimum attenuation of at least 10 dB is maintained above 0.65 GHz (1.82:1 tuning ratio).