High Selective Bandpass Filter With Controllable Transmission Zeros

This paper proposed a high selective bandpass filter with independently controllable transmission zeros (TZs). By using interdigital capacitors and common shorted stubs, two mixed couplings in opposite signs are realized between adjacent stepped impedance resonators (SIRs). Through changing the finger length of the interdigital capacitor or the common grounded stub, the TZs can be controlled independently. Meanwhile, two shorted stubs are introduced to suppress the first parasitic passband. Thus, higher selectivity and wider stopband are achieved. To verify our design method, one experimental filter is fabricated.