Tunable high quality-factor absorptive bandstop filter design

A two-pole, substrate-integrated, high quality(Q)-factor absorptive bandstop filter is demonstrated that exhibits enhanced selectivity over traditional reflective bandstop filter designs and higher Q-factor components than previous absorptive designs. With a Q-factor of 729, the presented filter has a peak isolation of 30 dB, a narrow 10-dB rejection bandwidth of 3.9 MHz that is tunable over 3.4–3.8 GHz, and an out-ofband insertion loss of 0.3 dB, exhibiting the same attenuation of a standard two-pole reflective notch filter with a Q-factor of 3100. These features enable channel-select isolation of high power interfering signals from closely separated receive bands without impacting receiver noise figure.