Ultra-Wideband Microstrip-Line Bandpass Filters with Good Out-of-Band Performance using EBG-Embedded Multiple-Mode Resonator

A class of ultra-wideband microstrip-line bandpass filters with improved out-of-band performance and miniaturized size is proposed and constituted using electromagnetic-bandgap (EBG) embedded multiple-mode resonator (MMR). This EBG- embedded MMR is at first studied, aiming to relocate its first three resonant modes within the 3.1-10.6GHz UWB passband while inhibiting its 5th resonant mode in the upper frequency range. Moreover, the coupling zero of external coupled-lines is properly adjusted to cancel the excitation of the 4th resonator of this MMR. A single-stage bandpass filter is then investigated to initially demonstrate the improved UWB bandpass behavior. Afterwards, two- and three-stage bandpass filters are designed to further sharpen out-of-band rejection skirts and deepen lower/upper stopbands as required by FCC-defined UWB mask. Finally, three filter samples are fabricated and tested. It is shown that the measured results are well matched to the predicted ones in terms of insertion/return losses and group delay over the plotted frequency range of 1.0 to 20.0GHz.