Compact and High Selectivity Cross-Coupled Broadband Microstrip Bandpass Filter

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. (c) 2013 Wiley Periodicals, Inc.