This paper proposes a new microstrip stepped-impedance resonator (SIR) used for bandpass filters with reduced size and improved stopband characteristics. A comprehensive treatment of both ends of the resonator with loaded triangular and rectangular microstrips is described. The design concept is demonstrated by two filter examples including four-resonator parallel-coupled Chebyshev bandpass and compact four-resonator cross-coupled elliptic-type filters. These filters are not only compact size due to the slow-wave effect, but also have a wider upper stopband resulting from the resonator bandstop characteristic. The filter designs are described in details. The simulated and experimental results are demonstrated and discussed.

New microstrip bandpass filters with extended stopband bandwidths are proposed by using new asymmetric stepped-impedance hairpin resonators (ASIHRs). The size of the proposed resonators has been reduced around 16%, comparing with the conventional stepped-impedance hairpin resonators (SIHRs) structure. The first bandpass filter is a combination of differ resonators with the same fundamental frequency but differ in harmonic frequencies, resulting in improved suppression spurious responses in stopbands. Furthermore, another bandpass filter uses the ASIHRs periodically loaded on a microstrip line to improve stopband characteristics. The proposed filters not only have compact size of resonators, but also provide improved upper stopband characteristics. The proposed filters provide 20 dB rejection levels in the stopband up to 6f0. The measured filters responses agree very well with the simulated expectations.