Ultra-Compact Ultra-Wideband Bandpass Filter Based on Multi Mode Resonator Concept

An ultra-compact ultra-wide band (UWB) bandpass filter (BPF) with a very sharp rejection for the high-speed wireless communication applications is proposed. Thefunctional basis of the proposed structure is based on the multi-mode resonator (MMR)technique. The suggested ultra-wideband filter is realized by using two doublet parallelcoupling lines, two symmetrical open stubs and tri-section step-impedance open stubswhich are located at the center of the configuration. In order to analyze the suggestedconfiguration, the even-mode and odd-mode methods have been utilized because of theproposed UWB BPF is a symmetrical structure. Five modes which are including threeeven modes and two odd modes have been placed within the UWB band. By changing thedimensions of the tri-section step-impedance open stubs and two symmetrical open stubs,the resonant modes of the constructed MMR can be tuned. These two parts have beenmainly applied to adjust the resonant modes into desired passband. Changing thedimensions of the two symmetrical open stubs affects both the even and odd modes. Butthe tri-section step-impedance open stubs can only specially control the even-moderesonant frequencies, whereas the odd-mode ones are fixed. Consequently, the centerfrequency and the bandwidth of the proposed configuration can be simply adjusted.Experimental verification is provided and a reasonable agreement between simulated andmeasured results has been achieved. The proposed UWB BPF has a passband covers 3.55to 10.65 GHz and the measured 3 dB fractional bandwidth (FBW) is about 100%.