A two-stage SIR bandpass filter with an ultra-wide upper rejection band

Abstract

Two-stage stepped-impedance resonator (SIR) filters are designed to have a wide upper stopband. Two transmission zeros are also created near the passband to form a quasi-elliptic response. For a 20-dB rejection level, with properly designed SIR geometry and tapped-line structure, the leading three spurious re nances of the SIR are suppressed by transmission zeros and respective unmatched singly loaded Q (Q(si)) values. Measured results illustrate that stopbands up to 8.4 and 5.3 times the design frequency can be achieved for rejection levels of 20 and 30 dB, respectively.