Highly-miniaturized packaged UWB 7th-order bandpass filter

This paper describes an original filtering solution for specifications in the Ultra Wide Band (UWB) (3.1 to 10.6 GHz). This 7^th-order filter is based on an association of series- and parallel-resonators, where open-ended coupled-lines are used as series resonators, and open-ended stepped-impedance half-wavelength stubs as the parallel ones. Addition of open-ended half-wavelength stubs enhanced the rejection level close to the band edges. This UWB filter was realized in microstrip technology on a 254-μm-thick alumina substrate of permittivity 9.9. It was also strongly miniaturized to be put in a 0.32 × 0.32 inch² Stratedge package and mounted on a FR4 plate for measurements: its insertion loss is 5 dB, and rejection in the lower and the upper bands is 31 and 20 dB, respectively. The measured return losses are better than 11.8 dB.