Tunable Reflectionless Filter With Independently Controllable Dual Passbands and Absorbed Harmonic Signals

A novel tunable reflectionless dual-passband filter (T-RDBPF) based on a single multi-mode resonator and absorptive networks is proposed firstly with independently tunable passbands, no reflection at full band, as well as absorbed harmonic signals. By increasing the admittance radios between parallel resonant paths in the multi-mode resonator, two individually controlled passbands with independent poles can be achieved. To correspond to the resonant poles, two series resonant loops are employed to generate independent zeros in the absorptive network, thus consecutive reflection absorptivity for all tuning states is realized. Without deploying any other structure, the absorptive network for out-of-band signals being equivalent to a resistor, is reused to provide an additional transmission path to absorb multiple harmonics. Then, both the transmission and reflection of harmonics are suppressed. Measurement results show that the proposed tunable reflectionless filter features two independent tuning ranges of 1.45–1.95 GHz (f ₁) and 2.45–3 GHz (f ₂), a minimum absorption level of −6 dB @f ₁& −7.3 dB@f ₂from DC to 6 GHz, a minimum harmonic absorption of −5.8 dB (S11) and −13.9 dB (S21) @ up to7.4f ₁respectively.