Compact and High Selectivity Cross-Coupled Broadband Microstrip Bandpass Filter

ABSTRACT In this article, a new compact and high selectivity broadband microstrip bandpass filter (BPF) is proposed using one folded half‐wavelength resonator (FHWR) in the middle and two quarter‐wavelength resonators (QWRs). Due to the cross coupling between the source/load and FHWR, four transmission zeros can be created in the lower‐ and upper‐stopband. The transmission zero generated by the coupling between the QWR and parallel‐coupling feedline can sharpen the skirt and suppress the first harmonic of the FHWR. To verify the design concept, a microstrip BPF with 1‐dB fractional bandwidth (FBW) of 61% centered at 3 GHz is designed and fabricated. Measured results show low insertion loss and flat group delay in the entire passband as well as high out‐band rejection. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2501–2504, 2013